In brake systems of rail vehicles, the friction conditions between wheel or wheelset and rail, or between the brake disk and the brake pad assigned to the brake disk, fluctuate in a manner dependent on weather conditions, ambient temperature, state of wear and load profile, with the fluctuation sometimes being considerable. If it is now sought to regulate a braking torque acting on a wheelset of a rail vehicle, the braking torque generated by way of a brake caliper of a brake system should be measured with adequate accuracy. The braking torque generated at a brake disk is however dependent on a wide variety of factors such as, for example, a contact pressure force between pads and brake disk, a friction coefficient between the brake pad and a brake disk, or a friction radius which represents the spacing between the resultant friction force and the axis of the wheelset.
Since both a local contact pressure between the brake pad and the brake disk and also the friction coefficient of the brake pad on the brake disk are dependent on a multiplicity of factors (which in some cases exhibit high local variation), the friction radius is also not a fixed, unchanging value, which is however required for the regulation of the braking torque to be applied. Rather, during successive braking operations, fluctuations of the friction radius occur which cannot be disregarded. Causes for this include, for example, different starting temperatures of brake disk and brake pad, a different starting speed, a varying surface condition of the brake pad owing to thermal deformation, and/or wear of brake disk and brake pad.
The braking torque acting on a brake disk generally corresponds to the product of contact pressure force of the brake pads against the brake disk, the friction coefficient between the brake pad and the brake disk, and the present (possibly rapidly changing) friction radius.
If only the circumferential force is measured, which corresponds to a friction force acting on the brake disk, and the friction radius is assumed to be constant, the braking torque can be measured with only relatively low accuracy.
Disclosed embodiments provide for improved detection of a braking torque and thus for the control of a braking force with high accuracy.
Disclosed embodiments provide a method for determining a braking torque at a brake system for a rail vehicle, a method for outputting a braking signal for a braking force at a brake system for a rail vehicle, an apparatus for determining a braking torque at a brake system for a rail vehicle, and an apparatus for outputting a braking signal for a braking force at a brake system for a rail vehicle.